Method for transposing a surface pressure field from a mesh modeling a turbomachine part to another mesh

ABSTRACT

Method for transposing a surface pressure field from a first mesh modeling a turbomachine part to a second mesh different from the first mesh, comprising steps of: calculating (100) pseudo-pressure values (P10, P20-P25) at vertices or edges of the first mesh, based on pressure values (P11-P16) of the surface pressure field respectively associated with faces of the first mesh, transposing the calculated pseudo-pressure values to the second mesh by an interpolation tool, so as to generate pseudo-pressure values (P30-P32, P40-P42) at vertices or edges of the second mesh, and for at least one face of the second mesh, calculating a pressure value (P50) associated with the face based on the pseudo-pressure values (P30-P32, P40-P42) generated at vertices or edges delimiting the face of the second mesh.

FIELD OF THE INVENTION

The present invention relates to the field of computer modeling ofmechanical parts. It advantageously finds application for modelingturbomachine parts.

STATE OF THE ART

In order to define the shape of a turbomachine part, the pressure thatsuch a part may undergo during the operation of the turbomachine isusually taken into account.

For that purpose, the part is modeled in the form of a mesh comprisingvertices and edges defining faces. Among these faces, some faces, calledfree faces, are representative of free surface portions of the part.

A surface pressure field is also developed. The surface pressure fieldcomprises a plurality of pressure values, each pressure value beingassociated with one of the free faces of the mesh.

Achieving this association of a pressure value with each free face ofthe mesh requires a lot of time and know-how. Indeed, to achieve such anassociation, it is necessary to model a flow acting on the part, whichis complex. It is also necessary to carry out a zoning work, consistingin segmenting the mesh into different portions, which is tedious andlong. Generally, obtaining a surface pressure field is thus entrusted tospecialized experts.

These surface pressure fields can then be used by other teams of peoplewho exploit such surface pressure fields for finite element modeling,whose purpose is to determine the mechanical behavior of the part, butwho are not such specialized experts.

However, in some situations, a non-specialized person may realize thatthe mesh for which he has a surface pressure field is not optimal, andmust therefore be modified. For example, a zone of the considered partcan comprise an insufficient number of faces, in which case this personmust add such faces in the mesh.

However, the surface pressure field is no longer adapted to the modifiedmesh. And requesting an expert to regenerate a new surface pressurefield adapted to the modified mesh is obviously long and therefore veryexpensive.

DISCLOSURE OF THE INVENTION

An aim of the invention is to be able to transpose a surface pressurefield from a first mesh modeling a turbomachine part to a second meshmodeling the same part but being different from the first mesh, in a waythat is fast and inexpensive.

To this end, there is proposed, according to a first aspect, a methodfor transposing a surface pressure field from a first mesh modeling aturbomachine part to a second mesh different from the first mesh, inwhich the surface pressure field comprises pressure values respectivelyassociated with faces of the first mesh, the method comprising thefollowing steps implemented by computer:

a) calculating pseudo-pressure values at vertices and/or edges of thefirst mesh, each pseudo-pressure value at a vertex or an edge beingcalculated based on pressure values of the surface pressure fieldrespectively associated with faces of the first mesh delimited by thevertex or the edge,

b) transposing the pseudo-pressure values calculated in step a) from thefirst mesh to the second mesh by a thermal field interpolation tool, soas to generate pseudo-pressure values at vertices and/or edges of thesecond mesh,

c) for at least one face of the second mesh, calculating a pressurevalue associated with the face based on the pseudo-pressure valuesgenerated in step b) at vertices and/or edges delimiting the face of thesecond mesh.

The first mesh and the second mesh each define:

-   -   free faces representative of free surface portions of the part        and    -   internal faces representative of zones crossing the part,

in which step a) is implemented to calculate pseudo-pressure values atvertices and/or edges selectively associated with free faces of thefirst mesh but not with internal faces of the first mesh, and/or inwhich step c) is implemented selectively on free faces of the secondmesh and not on internal faces of the second mesh.

Thanks to these selective calculations, the duration of implementationof the transposition method is much shorter than the one required toregenerate a complete mesh in the way described in the introduction.

The method according to the first aspect can optionally comprise thefollowing characteristics, taken alone or combined together when this istechnically possible.

The method according to the first aspect can cleverly take advantage ofthe fact that a thermal field interpolation tool is already known,making it possible to transpose thermal fields from one mesh to theother. The method makes it possible to divert this tool from its primaryuse, by injecting it not with temperatures but with pressures. However,a surface pressure field defines pressures at mesh faces, while thistool takes as input temperatures at mesh vertices or edges, hence theimplementation of steps a) and c).

Preferably, a pseudo-pressure value calculated in step a) at a vertex orat an edge is an average of pressure values of the surface pressurefield respectively associated with faces of the first mesh delimited bythe vertex or the edge.

Preferably, the method comprises a heat transfer calculation taking thepseudo-pressure values calculated in step a) as initial conditions, soas to obtain temperature values at vertices and/or edges of the firstmesh, the temperature values being passed as input to the interpolationtool.

Preferably, a pressure value associated with a face of the second meshand calculated in step c) is an average of pseudo-pressure valuesgenerated in step b).

Preferably the first mesh and the second mesh each define:

-   -   free faces representative of free surface portions of the part,        and    -   internal faces representative of zones crossing the part,

and step a) is selectively implemented to calculate pseudo-pressurevalues at vertices and/or edges of free faces of the first mesh, and/orin which step c) is selectively implemented on free faces of the secondmesh.

Preferably, at least one of the first mesh and of the second mesh is atetrahedral mesh.

Preferably, at least one of the first mesh is of degree 2.

Preferably, the part is a portion of a high-pressure turbine of theturbomachine, for example a blading.

Also proposed are: a computer program product comprising program codeinstructions for executing the steps of the method according to thefirst aspect, when this program is executed by a computer, as well as acomputer-readable memory storing instructions executable by the computerfor executing the steps of this method.

DESCRIPTION OF THE FIGURES

Other features, aims and advantages of the invention will emerge fromthe following description which is purely illustrative and not limitingand which should be read in relation to the appended drawings in which:

FIG. 1 schematically illustrates a device for transposing a surfacepressure field from one mesh to another, according to one embodiment ofthe invention.

FIG. 2 represents part of a first mesh and pressure values associatedwith faces of this first mesh.

FIG. 3 is a flowchart of steps of a method for transposing a surfacepressure field from one mesh to another, according to one embodiment ofthe invention.

FIG. 4 represents the same mesh part as the one represented in FIG. 2 aswell as pseudo-pressure values calculated in different elements of thismesh.

FIG. 5 represents part of a second mesh, and pressure or pseudo-pressurevalues associated with different elements of this second mesh.

In all of the figures, similar elements bear identical references.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a device 1 for transposing a surface pressure fieldcomprises at least one processor 2 and one memory 4.

The device 1 is for example a computer to be used for finite elementmodeling. It can therefore comprise a screen and an input interface(mouse, keyboard, touch sensitive element, etc.).

There is stored in the memory 4 a transposition program comprising codeinstructions for executing a method which will be described below.

In other words, memory 4 is a non-transitory computer-readable mediumcomprising code instructions of the transposition program.

The transposition program comprises an interpolation tool or isconfigured to interact with such a tool.

In the following, the non-limiting example of an interpolation toolsuitable for interpolating a thermal field is considered.

The processor 2 is configured to execute this transposition program. Theprocessor may be of any type: a CPU, a circuit such as an ASIC, areprogrammable circuit such as an FPGA, etc.

Data representative of a first mesh are also stored in the memory 4, thefirst mesh being itself representative of a turbomachine part.

This part is typically a portion of a high-pressure turbine of aturbomachine.

The first mesh comprises of a plurality of vertices (also called nodes).Each vertex has a 3D position specific thereto.

Some pairs of vertices of the first mesh are linked by an edge.

The first mesh furthermore comprises cells connecting the vertices toeach other.

The first mesh is a 3D mesh in the sense that these cells are polyhedracomprising a plurality of faces.

These polyhedra are for example tetrahedra (in this case, the faces aretriangular).

Each face is definitively delimited by vertices and by edges of thefirst mesh. More specifically, each polygonal face is defined by andbetween at least three vertices (forming the vertices of the face) andat least three edges (forming the sides of the face).

The first mesh is also for example of order 2.

There are two types of faces in the first mesh: faces, known as “free”faces, representative of portions of surfaces of the considered part,and faces known as “internal” faces, crossing the part.

By way of example, FIG. 2 represents six free faces of the first mesh. Avertex of this first mesh constitutes a vertex of each of these faces,which are here triangular, or an edge in the case of a mesh of degree 2.

A surface pressure field associated with the first mesh is also storedin the memory. The surface pressure field comprises a plurality ofpressure values. Each of these pressure values is associated with one ofthe free faces of the first mesh: it represents a pressure value thatthe part is able to undergo in a portion of surface modeled by theassociated face.

The surface pressure field can also comprise zero pressure values whichare associated with the internal faces of the first mesh. As a variant,the internal faces of the first mesh are not associated with pressurevalues of the surface pressure field.

As indicated in the introduction, the first mesh and the associatedsurface pressure field are developed jointly by an expert, according toa method known from the state of the art requiring a lot of time (up to3 weeks for a part of very complex shape).

The pressure values of the surface pressure field which are associatedrespectively with the faces represented in FIG. 2 are referenced P11 toP16.

Data representative of a second mesh are also stored in the memory 4,this second mesh itself being representative of the same part as thefirst mesh, or of a slightly different turbomachine part. The secondmesh is different from the first mesh. This implies that the second meshcomprises more vertices than the first mesh or fewer vertices than thefirst mesh or that vertices of the second mesh have positions differentfrom those of the first mesh.

The second mesh has for example been generated by a program based on thefirst mesh, by deleting or moving at least one vertex of the first meshor by adding at least one new vertex in the first mesh. Such amodification can in particular be carried out using the ANSA program.

With reference to FIG. 3, the following steps are implemented by thetransposition program, when this program is executed by the processor 2of the device 1, to obtain a new surface pressure field adapted to thesecond mesh.

During a step 100, the processor 2 calculates pseudo-pressure values atvertices and/or edges of the first mesh, each pseudo-pressure value at avertex or an edge being calculated based on pressure values of thesurface pressure field respectively associated with faces of the firstmesh delimited by the vertex or the edge.

FIG. 4 represents the following data calculated during step 100: apseudo-pressure P10 calculated at the vertex linking the six facesrepresented in FIG. 2, as well as pseudo-pressures P21-P25 calculated atthe edges linking these six faces two by two.

To obtain a pressure value at a vertex of the mesh, the average ofpressure values of the surface pressure field respectively associatedwith faces of the first mesh having the considered vertex as a vertex isfor example calculated. Preferably, all the faces of the first meshhaving the vertex considered as vertex are taken into account.

Thus we have: P10=(P11+P12+P13+P14+P15+P16)/6.

To obtain a pressure value at an edge of the mesh, the average ofpressure values of the surface pressure field respectively associatedwith faces of the first mesh having the edge as a side is calculated.

Thus we have:

P20=(P16+P11)/2

P21=(P11+P12)/2

P22=(P12+P13)/2

P23=(P13+P14)/2

P24=(P14+P15)/2

P25=(P15+P16)/2

In the embodiment illustrated in FIGS. 2 and 4, the pseudo-pressurevalues are thus calculated in the form of arithmetic means, but othertypes of calculations can be considered (other types of means, linearcombination, etc.).

Step 100 is implemented for different vertices or edges delimited byfree surfaces of the first mesh.

The processor then implements a heat transfer calculation taking thepseudo-pressure values calculated in step 100 as initial conditions, soas to obtain temperature values at vertices and/or edges of the firstmesh.

The temperature values are then passed as input to the thermal fieldinterpolation tool, along with the first mesh and the second mesh.

During a transposition step 102, the interpolation tool generates, byinterpolation of these input data, pseudo-pressure values associatedwith vertices and/or edges of the second mesh. At least one face whosevertices and/or sides are associated with pseudo-pressure values arethus found in the second mesh.

This generation is implemented for all the free faces of the secondmesh, even for all the faces of the second mesh.

A face of the second mesh is represented by way of example in FIG. 5.This triangular face comprises three vertices corresponding to threevertices of the second mesh, and three sides corresponding to threeedges of the mesh. During the transposition step 102, were generated bythe thermal field interpolation tool: pseudo-pressure values P30 to P32at these vertices and pseudo-pressure values P40 to P42 at these edges.

In a step 104, the processor 2 uses these pseudo-pressure values toobtain a new surface pressure field associated with the second mesh. Forthat purpose, the processor 2 calculates for at least one face of thesecond mesh, a pressure value associated with the face, based onpseudo-pressure values generated by the interpolation tool at verticesand/or edges of the second mesh that delimit this face.

For example, a pressure value P50 calculated for the face represented inFIG. 5 depends on the pseudo-pressure values P30 to P32 at the threevertices of this face and on the pseudo-pressure values P40 to P42calculated at the three sides of this face.

Preferably, the calculation carried out is an average of all or part ofthese pseudo-pressure values. Therefore, we have for example, in thecase of an arithmetic mean:

P50=(P30+P31+P32+P40+P41+P42)/6

This step 104 is conducted on several free faces of the second mesh, oreven all of them. Preferably, this step is selectively implemented onfree faces of the second mesh.

The duration of implementation of the steps of the aforementioned methodis much shorter than the one required to regenerate a complete mesh inthe way described in the introduction (less than 30 minutes versusseveral weeks).

The method described above can also be the subject of other variants. Inparticular, only pseudo-pressures at face vertices can be calculatedduring step 100 and/or 104. As a variant, only pseudo-pressures at faceedges can be calculated during step 100 and/or 104. But calculatingpseudo-pressures at vertices and faces, as illustrated in FIGS. 4 and 5,allows transposing in a finer and more precise manner a surface pressurefield from the first mesh to the second mesh.

1. A computer-implemented method comprising: in a step a), calculatingfirst pseudo-pressure values at vertices and/or edges of a first meshmodeling a turbomachine part, wherein each of the first pseudo-pressurevalues is calculated based on input pressure values of a surfacepressure field, and wherein the input pressure values are respectivelyassociated with faces of the first mesh, in a step b), transposing thefirst pseudo-pressure values from the first mesh to a second meshdifferent from the first mesh by an interpolation tool, so as togenerate second pseudo-pressure values at vertices and/or edges of thesecond mesh, in a step c), calculating output pressure values associatedwith faces of the second mesh based on the second pseudo-pressurevalues, wherein the first mesh and the second mesh each define freefaces representative of free surface portions of the part, and internalfaces representative of zones crossing the part, and wherein all thefirst pseudo-pressure calculated at step a) are associated with onlyfree faces of the first mesh and/or all output pressure valuescalculated at step c) are associated with only free faces of the secondmesh.
 2. The method of claim 1, wherein at least one of the firstpseudo-pressure values is an average of input pressure values of thesurface pressure field.
 3. The method of claim 1, wherein theinterpolation tool is suitable for also interpolating a thermal field.4. The method of claim 1, comprising calculating a heat transfer takingthe first pseudo-pressure values as initial conditions, so as to obtaintemperature values at vertices and/or edges of the first mesh, thetemperature values being inputted in the interpolation tool.
 5. Themethod of claim 1, wherein at least one of the output pressure values isan average of second pseudo-pressure values.
 6. The method of claim 1,wherein at least one of the first mesh and of the second mesh is atetrahedral mesh.
 7. The method of claim 1, wherein at least one of thefirst mesh and the second mesh is of degree
 2. 8. The method of claim 1,wherein the part is a portion of a high-pressure turbine of theturbomachine.
 9. The method of claim 1, wherein the part is a portion ofa blade of a high-pressure turbine.
 10. A non-transitorycomputer-readable medium comprising code instructions for causing acomputer to perform the method of claim 1.